Production of acrolein



esistiti l stessi esoooouiou oe soeoueut nei-i eea-stem osseuse, u, u,osseuse to lesoieiu ilcsuoeetlon, u cosmsutlouot Eels-1 supuestos elleci, ieee, sessi' No. esisto This invention relates to improvements inthe production ci ecioleln from piopylene with the use oi on acidsolution contoiuinrg mercutio sulfate, known es Denises ieegeut.

It is known that propylene is absorbed vtoy Deniges ressent at etempera-.ture oi' about 85 C. with the production oi e yellowprecipitate which on further heating oecomposes with liberation ofecrolein, lout no attempt Boos heietoore 7izeeo mafie, so ier es Ieivsu' to produce eoiolein, except es o, laboratory experiment, in thiswey.

The present invention provides en improved method for the production oiectolein in e prec,- tical way, with advantageous utilization ci thereagent and regeneration thereof suoi with the production oi ecrolein cihigh purity in on oelvantsgeous :mennen Deniges reagent is prepared fromabout 5 parts icy weight of mercurio oxide, about 36.8 parte loy weightof sulfuric scid tot Re.) und about l0@ pests by tva-zieht of Water. TheocuI of propylene in the sesgent and subsequent lieB composition. leavesthe mercury reduced es niet curous sulfate enel ou scid solutioncontoicn= ing some organic metter enel lieving reducing properties. Themercurons sulfate iomieci is elversion of propylene into ecroleiu byabsorption most completely insoluble iu the liquid snol tenais c toseperate es e sludge oi' deposit.

The ovei'ell sciistico for the reaction involved in the production `ciscrolein imm ptooylene appears to be ss ioliowsi According to theimproved process of the present invention 7oi'opylene in excess isbrought into contact with the hot ressent to etect sub stentiell'ycomplete utilization of the reagent und decomposition of the resultingintermediate product is thereafter obteined with the use ot 4of enintermediate precipitate omi the clecom position of this precipitate on:further nesting to form ecroleiu suo. niercurous sulfate., Theosea.;-zz ent invention provides en improved method for bringing stout'these seecticus so thet they muy im, 2MB-mmm) be advantageouslycombined es port of e single complete operation.

The mixture oi psogoylene and ocrolein is subseuuently treated tosepsis-te the scroleln from the propylene oudthe prom/iene thusseperated is returned to the process while the ecrolein is seperatelyrecoveieol. This separation of the eci'olelu from the propylene may losaccomplished ioy cooling und refrigeration to condense and llquefy theeci'olelu but it is advantageously oceomplished by scrubbing the mixedeases with cold water to slosorlo the ecrolein as an aqueous solutionfrom which the ucrolein con loe subsequently seperated by distillationto give acrolein of high purity.

The reagent used in the process is converted into an acid residual'liquor conteo' sing mercurous sulfate und with various organicimpurities. This residue contains practically all of the origincl coldused but is not adept/ed for further use in the process.` This residueeither as a, whole or after separation of its constituents may hetreated so that en additional amount of fresh reagent ceu loe producedtherefrom for further use in the process, thus making the process cycliciu nature by regenerating fresh reagent fiom the reagent residue.

Thus the scid sludge from the chemical reactions may be advantageouslysubjected to oxidation as e whole by the use of an electrolytic cell ofthe diaphragm type using en insoluble anode. By introducing the sludgeinto the anode chamber ci e listelli-ogm cell oud ley using e fairlyhigh current density the sludge is subjected to oxicletioii withconversion o the mercurous sulfete precipitate into mercurio sulfate insolution und et the same time organic matter present in the sludge isoxidized. The resulting oxidisco solution is similar in composition tothe oigiuul solution enel can advantageously be retumeoi fox reuse inthe process.

lustesd of subjecting the entire acid sludge to oxidation, this sludgecon be seperated and the mercuious sulfate precipitate separatelytreated. This precipitated mercurous sulfate, which is very dense undgranular, may loe separated by zlecentcttiou from its acid mother liquorand, oxiuizecl by treatment with nitric scid. When nitric acid isthusused the resulting oxides formed ceu he euveutegeouslyrecovered. Themercurous suliuise cen olso be oxidized by roasting unoler suitableconditions in the presence of en excess of oxygen for the iegenerstlonof mercurio sulfate. The scid mother liquor, from which the mercusoussuliste is seperated ici' seperate treetment, can similarly be subjectedto oxidation, .e. g., with nitric acid to remove or oxidlze organiccompounds and the resulting mother liquor can then be recombined withthe regenerated mercuric sulfate, thus regenerating the combined reagentfor reuse.

The invention will be further described in connection with theaccompanying drawing Awhich illustrates, in a conventional anddiagrammatic manner, a ow sheet or arrangement of apparatus and sequenceof steps adapted for use in practicing the process, but it will beunderstood that the invention is illustratedthereby but is not limitedthereto. In the accompanying drawing i 'I'he figure shows an arrangementfor practice of the process.

In the arrangement of the illustration two separate spray towers areshown, one for the absorption of the propylene in the reagent to formthe intermediate precipitate and the second for the further reaction ofthis intermediate precipitate with resulting formation of acrolein. Theiirst spray tower is shown as supplied with the reagent through apreheater by which it may be preheated to the proper temperature andwith both the reagent and the propylene entering at the top of the spraytower with intimate spraying of the re.- agent into the propylene andconcurrent ow of the solution and propylene through the tower, with thepropylene gas in considerable excess.

This concurrent flow offgas and liquid brings the fresh reagent intocontact with the propylene and prevents it from coming into contact withany acrolein such as might take place with a countercurrent flow.

At the bottom of the rst tower the excess propylene is taken oir througha water scrubber trap where it is scrubbed with water to remove anyacrolein that may be contained in it and the resulting propylene is thenshown as being returned to the propylene supply or alternately it may besupplied to the second spray tower.

trated and the diagrammatic arrangement of apparatus is not intended toshow the parts to scale but it is intended to be illustrative of thetypes of towers, etc. which can advantageously be used in the process.

The spray towers are unpacked towers. 'I 'he packed stripping tower isiilled with suitable packing material so that the gases will beintimately washed by the cold water running down over the packing toinsure substantially complete scrubbing of the acrolein from the mixedgases The acid sludge from the rst spray/tower containing the productsresulting from the reaction between the propylene and the acid mercuricsulfate reagent, is pumped to the.top of another tower and again sprayedinto the tower countercurrent to a rapid stream of propylene gasentering near the bottom. 'I'he time taken in pumping the sludge fromthe bottom of the first tower to the second can be so regulated thatthedesired decomposition will have largely taken place before the sludgeenters the second spray tower and the acrolein thus liberated and whichescapes in the second tower is swept out by the current oi propylene andthe mixture of propylene and acrolein `is shown as going to a packedstripping tower where the acrolein is absorbed in cold water and thepropylene freed from acroelein for return to the process or to thepropylene supply either directly or through a preheater in heatinterchanging relation with the hot propylene and acrolein vapors comingfrom the second spray tower.

The solution of acrolein in water coming from the packed stripping towertogether with the scrubbing water from the waterscrubber trap arecombinedand introduced into a heated stripping tower or still where theacrolein is distilled from its water solution.

The method of regenerating the acid sludge from the second spray toweris shown as by electrolytic cells of which three are illustrated but ofwhich any desired number can be used.

It will be understood that the :dow sheet illusso that the acrolein willbe recovered in water solution at the bottom of the tower, leaving thepropylene available for recycling. The heated stripping tower or columnmay be made up of Iractionating plates in which the acrolein isrecovered at the head and pure water at the bottom. With a suitabletower the acrolein can be recovered in substantially anhydrous formsince it forms no constant boiling mixture with water vapor and theboiling points are approximately 40 apart. i

The temperature during the first stage of the process, i. e., theinitial reaction between the propylene and the acid mercuric surfatereagent, is advantageously around 85 C. and in general should not behigher than about 105 C. During the next stage of the process, that is,the separation of acrolein from the reaction mixture, any suitabletemperature may be employed. Advantageously, the same temperature thatwas employed in the first stage of the process may be used, or thetemperature may be somewhat lower. The rstvoperation can be carried outat atmospheric pressure, but it can advantageously be carried out atsomewhat higher pressures of the order of 2 or 3 atmospheres witheconomy of space in the towers. It is one advantage of the process thatextreme high pressures are not required.

Acrolein, especially in the presence of the acid mercuric sulfatereagent, is readily decomposed if kept at high temperatures for anyvconsiderable length of time. It is one advantage of the present processthat the acrolein is rapidly removed from the high temperature part ofthe apparatus by the current of propylene so that objectionabledecomposition is obviated or minimized.

Although an intermediate precipitate is formed by absorptionl of thepropylene and although the sludge resulting from the decomposition ofthis precipitate also contains a precipitate (the mercurous sulfate)these precipitates and the sludges containing them are advantageouslyhandled in the present process. In the arrangement shown the spraying ofthe reagent brings about intimate contact of the reagent with the excessof propylene. and the sludge formed is readily handled by pumping andintroduced as a spray into the second tower from which the sludge canthen be transferred to the electrolytic cells or to other place oftreatment and regeneration of the reagent.

' In the operation of the process the reagent may be kept hot in thestorage tank but ordinarily it will be kept at a lower temperature andpreheated to the required temperature in a preheater before it isintroduced into the first spray tower. 'I'he spray towers are shown asunheated and with the heat supplied by the preheating of the solution;but further heating of the spray towers may be employed to maintain thedesired temperature.

The regeneration of the reagent may be either intermittent or continuousand where intermittent, as with the use of electrolytic cells foroxidizing the sludge, a suiilciently large number of cells can be used,and a suciently large amount of the reagent can be supplied to obtain ineect a substantially continuous operation. The re-l generation of thereagent makes it unnecessary to supply new reagent except to make up forlosses and to adjust the composition of the reagent from time to time ifrequired. Should the reagent after repeated regeneration and reusebecome contaminated, the regeneration ofthe sludge as a whole may bereplaced by separation of the mercurous sulfate precipitate and itsseparate oxidation to form mercuric or oxyrnercuric sulfate and byseparately purifying the waste acid, or replacing it with fresh acid.

In the foregoing description of my process propylene has been used as aconvenient medium for sweeping acrolein out of the reaction mixture. Itshould be understood, however, that, in general, any gas or vapor whichdoes not destroy acrolein may be used for this purpose, for example,water vapor, carbon dioxide, nitrogen or suitable hydrocarbons, etc.,may be used.

It will thus be seen that the invention provides an improved andadvantageous method for the production of acrolein in a simple andadvantageous manner and with continuous operation, in which the reagentscan be regenerated and repeatedly reused and in which the propylene isadvantageously employed in large excess in the process, with advantagessuch as those hereinbefore referred to.

I claim:

'Ihe continuous method of producing acrolein whic-h comprisescontinuously spraying a' hot aqueous mercurio sulfate reagent into acurrent of propylene, with concurrent ow of the spray and gas andproduction of an intermediate reaction product in suspension,continuously spraying the resulting suspension with accompanyingdecomposition into a current of propylene countercurrent thereto,whereby the acrolein is removed in admixture with propylene, andsubsequently treating the admixed propylene and acrolein to separate theacrolein therefrom.

KARL M. HERSTEIN.

